1. Field of the Invention
The present invention relates to an improved tappet assembly interposed between an overhead cam shaft and the stem of a standard poppet valve of an internal combustion engine. Such assembly is self-operating to eliminate valve lash when the engine is running at its normal operating temperature.
2. Prior Art
The tappet assembly of an overhead cam internal combustion engine commonly includes an inverted cup follower fitted in a cylindrical bore of the cylinder head in line with the upward-projecting stem of a valve. Shims can be used to achieve a desired clearance between the top end of the valve stem and the underside of the cup. The top of the cup is engaged by a lobe of the cam shaft. Ideally, the clearance is set and periodically adjusted such that valve lash is eliminated, i.e., the clearance is zero, when the engine reaches its normal operating temperature. It can be time-consuming, painstaking work to set or adjust the clearance by use of shims of different thicknesses.
More complicated tappet assemblies use screws to move wedgelike shims or to compress elastomeric shims, such as the assemblies disclosed in Jensen U.S. Pat. No. 3,538,895, issued Nov. 10, 1970, Line U.S. Pat. No. 3,818,879, issued June 25, 1974, and Morgan U.S. Pat. No. 3,989,016, issued Nov. 2, 1976. Still, the screws must be turned manually to adjust the valve clearance. Achieving the ideal clearance requires partial disassembly of the engine and the experience and technique of a skilled mechanic.
Representative tappet assemblies intended to be self-adjusting are shown in Saives U.S. Pat. No. 1,733,240, issued Oct. 29, 1929, and Campbell U.S. Pat. No. 2,747,559, issued May 29, 1956.